This invention relates to tufting machines and more particularly to the detection of broken yarn ends adjacent the needles.
In a tufting machine more than 1,000 needles each carrying an individual yarn is employed for penetrating a backing material to insert loops of yarn therein, the loops being seized by a looper. Because of defects in the yarn itself or because of excessive tension or friction or other conditions, yarn breaks frequently occur before the yarn is stitched into the backing. When this occurs the product is defective and must be repaired as soon as the defect is detected. In high speed machines, however, in some instances the defect goes undetected or is difficult to repair, especially when the gauge is fine. Thus, the machine must be stopped to repair the defect if detected or the product must be discarded if it has gone undetected and is subsequently processed.
It is known in the prior art to detect broken yarn ends and to stop the machine upon occurrence of a break. For example, Jackson U.S. Pat. No. 3,529,560 and Merkle U.S. Pat. No. 3,764,773 disclose electromechanical devices having yarn supporting feelers or drop wires which drop when the yarn breaks to stop the machine. Other patents disclose electromechanical devices to shut the machine upon the detection of a high tension in the running yarn. These known electromechanical devices not only involve a large number of moving parts but are difficult to adjust and maintain. Moreover, because of their constructions, the known prior art devices have been mounted high up on the head of the tufting machine.
Ideally the broken yarn end detector should be placed between the feed means and the loop seizing location, and at least as close to the needles as possible so that a broken yarn can be detected at or adjacent the formation of the stitch such that a minimum amount of wasted fabric would be produced. This is particularly true in high speed tufting machines where subsequent mending is difficult. However, the aforesaid yarn supporting drop wires of the prior art were placed high up on the head of the tufting machine so as not to hinder a worker in threading yarn through the needles of the machine and making necessary adjustments including the replacement of broken needles. This is especially true when the yarn is not yet threaded through most of the drop wires and the wires are in the dropped position.
Thus, light beam devices were developed which could be placed closer to the needle location. In Jackson U.S. Pat. No. 3,687,095 one or two light beams are transmitted longitudinally across a tufting machine to photo-conductive receivers. When a yarn is broken, either a broken yarn end will fall into the light beam or a loop of yarn will be formed to enter the light beam and break the beam to interrupt current flow through a triggering circuit to deenergize the machine motor and shut the machine. Thus, proper operation of the device requires the broken yarn end or loop of yarn to enter the light beam. However, due to machine vibration and other operating conditions it is difficult to ensure that the yarn will enter the light beam when a break occurs, and this apparatus has not proved to be successful.